1. Field of the Invention
The present invention relates to an apparatus for controlling an engine, capable of detecting an abnormality in a power supply voltage supplied thereto.
2. Description of the Related Art
An apparatus for controlling an engine is supplied with power from a battery. The battery is charged by a generator mounted on a vehicle. The generator generates power when a field coil is excited with a field current and a power generation current is caused to flow through an armature coil rotating through rotation of the engine. Power generation control of the generator is performed by feedback control. That is, a control transistor is operated to be turned on and off to excite the field coil so that the voltage of the battery charged by the generator is held at a target voltage, and a target amount of power for making a voltage difference into zero is generated. The battery is charged through the power generation current, and the voltage of the battery is held at the target voltage.
When the output voltage of the generator has risen above an abnormally high voltage value, the field current is shut off to forcedly stop the power generation. Thus, the generator is protected from being destroyed through overcharge.
In order to detect an abnormality in a power supply voltage of the engine control apparatus, there is proposed a method using an ammeter (e.g., see JP 2001-69681 A).
However, the aforementioned protection against overcharge has the following problem. For instance, the engine control apparatus may operate by being supplied with power via a detour from a certain load terminal connected thereto when a power supply terminal of the engine control apparatus is disconnected. In this state, the power supply voltage supplied via the detour becomes lower than a normal power supply voltage due to a voltage drop. Accordingly, power generation control is performed based on this lowered power supply voltage, so the output voltage of the generator rises. While power generation can be forcedly stopped when the power supply voltage supplied via the detour is higher than an abnormally high voltage value, feedback control of the generator is performed when the output voltage of the generator is higher than the abnormally high voltage value but the power supply voltage supplied via the detour is equal to or lower than the abnormally high voltage value. Since power generation is then continued with the voltage higher than the abnormally high voltage value, the generator is destroyed through overcharge.
Further, since the ammeter is used as a detection unit, there is also a problem of high cost.